The Olympic Mudminnow

The Olympic Peninsula is home to a number of endemic species (you can find a complete list here). But there is only one endemic fish species that calls the region home: the Olympic mudminnow.

Novumbra hubbsi is the only species in the genus Novumbra and only one of five species in the family Umbridae, which also contains the eastern, central, and European mudminnows and the Alaska blackfish. Despite the name, mudminnows are more closely related to pickerel and pike than they are to minnows.

They are found in the coastal lowlands of Olympic Peninsula from Ozette Lake and the Queets River drainage to the north, the upper Chehalis River drainage to the south, and the Nisqually River to the east. They can also be found in lower Deschutes River (Puget Sound drainage) as a result of floodwater exchange with Chehalis River. Populations are present in King and Snohomish Counties, though these were likely introduced.

Olympic mudminnows were discovered by Grays Harbor County game warden John H. Winslow in 1921 when he found them in a drainage ditch near Satsop, a half-mile north of the Chehalis River, and sent specimens to the University of Washington College of Fisheries. The species was analyzed by ichthyologist Leonard P. Schultz in 1929. As he notes in his findings, they are unique from both a biological and geological standpoint due to their limited range (the smallest of any mudminnow species) and vast separation from the other members of Umbridae (Schultz 1929).

They are usually found in slow-moving streams, wetlands, marshes, and ponds. Within these habitats, mudminnows require a muddy bottom, little or no water flow, and abundant aquatic vegetation. They do not typically occur in area with large predatory fish, such as largemouth bass.  They are capable of surviving in environments with very low oxygen levels.

Olympic mudminnows are 2-3 inches long and brown in color. Their colors change during the mating season, when males become darker and get incandescent green and yellow stripes. They are carnivorous, eating a wide variety of benthic and aquatic invertebrates such as ostracods, isopods, oligochaetes, mysids, mollusks, and insect larvae (Nielson and Fuller 2012).

Spawning takes place between November and June. During this time, males establish their territories and become highly aggressive. They lure females onto their territory with a mating dance. The pair spawn several times as the female only releases one or two eggs per copulation. After all the eggs are released, the female is chased off the territory by the male. Eggs hatch after 10 days and remain attached to the vegetation until their yolk sac is absorbed. About seven days after hatching, they are able to swim. They receive no parental care, save the males chasing predators off their territories (Hagen, Moodie, and Moodie 1972).

They are considered to be of least concern by the International Union for the Conservation of Nature (ICUN) since they are found at over a hundred sites and total population, while not known, is estimated to be over 10,000 (NatureServe 2012). However, because they are endemic and susceptible to habitat loss, they are considered a sensitive species by the state of Washington.

It is likely Olympic mudminnows were more widespread before human occupation. An estimated 20-50 percent loss of suitable wetland habitat has occurred between settlement and the turn of the century. Their status as a sensitive species offers them some protections, but habitat loss is still a threat.

Research into these little fish has been sporadic over the past century and much about them remains unknown. These gaps in our knowledge make it difficult to provide adequate conservation efforts. However, there have been recent studies conducted at Green Cove Creek watershed in Olympia and Ozette Lake in the Olympic National Park and every new thing we learn about them helps this unique species thrive.

References

Hagen, D. W., Moodie, G. E., & Moodie, P. F. (1972). Territoriality and courtship in the Olympic mudminnow (Novumbra hubbsi). Canadian Journal of Zoology, 50(8). doi:10.1139/z72-148

Mongillo, P. E., & Hallock, M. (1999). Washington state status report for the Olympic Mudminnow. Retrieved February 03, 2021, from https://wdfw.wa.gov/publications/00221

NatureServe. (2012). Novumbra Hubbsi (Olympic Mudminnow). Retrieved February 04, 2021, from https://www.iucnredlist.org/species/14909/19034503

Nielson, M., & Fuller, P. (2012). Olympic Mudminnow (Novumbra hubbsi) - Species Profile. Retrieved February 04, 2021, from https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=976

Schultz, L. P. (1929). Description of a New Type of Mud-Minnow from Western Washington with Notes of Related Species. University of Washington Publications in Fisheries, 2(6).

US Fish and Wildlife Service. (2012). Olympic Mudminnow. Retrieved February 04, 2021, from https://wdfw.wa.gov/sites/default/files/2019-03/olympic_mudminnow.pdf

© Laura Caldwell, February 2021